1. Field
Example embodiments generally relate to fuel structures used in nuclear power plants and methods for using fuel structures.
2. Description of Related Art
Generally, nuclear power plants include a reactor core having fuel arranged therein to produce power by nuclear fission. The fuel elements may have a variety of configurations and/or characteristics, based on operating conditions of the specific nuclear power plant. For example, size, placement with respect to the core, placement relative to other fuel, enrichment, elemental fuel type, and shape of fuel all affect plant operating parameters. A common design in U.S. nuclear power plants is to arrange fuel in a plurality of cladded fuel rods bound together as a fuel assemblies placed within the reactor core.
As shown in FIG. 1, a conventional fuel bundle 10 of a nuclear reactor, such as a BWR, may include an outer channel 12 surrounding an upper tie plate 14 and a lower tie plate 16. A plurality of full length fuel rods 18 and/or part length fuel rods 19 may be arranged in a matrix within the fuel bundle 10 and pass through a plurality of spacers (also known as spacer grids) 20 vertically spaced one from the other and maintaining the rods 18, 19 in the given matrix thereof.
The fuel rods 18 and 19 are generally continuous from their base to terminal, which, in the case of the full length fuel rod 18, is from the lower tie plate 16 to the upper tie plate 14. Thus the cladding and fuel elements within the rod are also generally continuous through the length of the fuel rods 18 or 19.
As shown in FIG. 2, fuel elements 21 may be shaped in pellet-form and placed within the fuel rods 18 or 19. These fuel pellets 21 may be “stacked” within the fuel rod continuously to provide fuel through the length of the fuel rod 18 or 19. The stacking of fuel pellets 21 may permit expansion or other deformation of the fuel pellets 21 during the operation cycle of the reactor core. Further, a gap 22 between the pellets 21 and the inner wall 23 of the fuel rod 18 or 19 accommodates gaseous fission products produced from the fuel pellets 21 during operation of the reactor. The gap 22 may be a vacuum or filled with a low pressure, non-reactive gas such as Helium. Further gaps (not shown) and/or springs 24 at ends of the fuel rod may be present to further allow fission product accumulation and pellet deformation.